The present invention relates to improvements in paper forming machines, and more particularly to a machine for forming and bonding together plural plies of fibrous web, particularly for controlling the size of the water bead between the layers at the location where the plies come together.
In the formation of a multilayered paper web, individual layers are separately formed and brought together while wet to be bonded. Bonding is accomplished by an interlocking of the fibers on the confronting faces of the two layers, and optimum bonding forms the two layers to act as one so that a monolithic sheet results. The two layers can each contribute their own physical properties to the resultant sheet, and it is essential that a positive and uniform bond be completed over the entire surface of the layers.
It has been discovered that an improved bond will be augmented by the formation and maintenance of the bead of water in the nip between the layers as they are brought together. This bead probably acts as a conveying medium for small fiber ends to pass from one layer into the other layer and to there interlock. Where the lower layer is formed on the surface of a cylinder machine and the upper layer positioned over the first layer, suction is applied to the juxtaposed layer through the porous cylinder and additional water will pass downwardly from the upper layer to the lower layer to aid in the interlocking procedure. With the provision of a water bead between the layers, this moisture will pass downwardly into the lower layer forming a uniform interlock. It is essential to optimum plybonding that the bead of water be maintained at an optimum size. If the bead is of an insufficient size, it will not help the bonding between layers, or will help insufficiently to create the bond desired. If the bead is too large, it can act to adversely affect the orientation of the fibers and can keep the fibers between the layers apart so that actually a poorer bond results. When a bead of an optimum size is attained, it must be maintained for a given speed so that uniform bonding results, and the control of this bead size is important to the character and quality of the finished sheet of paper. The bead must be maintained uniform across the width of the paper, and control of various factors will increase or decrease the size of the bead. For example, the bead size will change with regulation of the stock density, the machine speed, suction in the forming cylinder, type of stock fiber, slice opening, fan pump pressure and other factors known to paper makers. However, this control must be accurately regulated, and the control operates best if it is not merely a function of the operating parameters of the machine, but operates to maintain a bead of the proper physical size. In other words, the change in the factors relating to the layers or to the speed of the machine are not as significant as the actual size of the water bead once an optimum size has been attained.
It is accordingly an object of the present invention to sense the size of a water bead between the nip of multiple layers in a paper making machine for making multilayered paper and to control and maintain the bead size to maintain an optimum moisture level for maximum bonding between plies.
A still further object of the invention is to provide a means for sensing and controlling the size of a water bead in bonding two layers of fibrous web wherein the size of the bead can be regulated to accommodate various changes in operating parameters and to maintain a bead of optimum desired size.
A further object of the invention is to provide a simplified construction which may be utilized on new paper making machines and can be installed and implemented as well on existing machines for detecting and controlling the size of the water bead for optimum plybonding.
Other objects, advantages and features, as well as equivalent structures and methods which are intended to be covered herein, will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings, in which: